Many computer systems and communication applications operate at multi-gigabit speeds. Such high speeds pose unique challenges to hardware designers, particularly with respect to multi-layer printed circuit boards. A printed circuit board (PCB) provides a compact means for routing signals between circuit components mounted on the PCB. However, printed circuit boards that support multi-gigabit/second digital signals require significant signal integrity. Signal integrity is a major issue not only in high-speed digital electronics, but also in high frequency RF systems. While a printed circuit board is efficient at creating a two-dimensional (planar) structure, a PCB is less efficient for three-dimensional structures.
A via is typically used to provide a connection between signal traces on different layers of the printed circuit board. For example, a via is needed to route signal traces between components mounted on opposite sides of the PCB. But, as signal frequencies increase, the wavelength of the signal decreases. Physical dimensions greater than, for example, 1/10th of a wavelength may degrade the signal as the signal propagates through a printed circuit board. Signal degradation results in unwanted signal loss, ripple, and distortion. Moreover, multiple traces on a densely routed PCB are often adjacent to each other, which causes unwanted signal coupling. Good shielding of the traces is required to prevent coupling.
Therefore, there is a need for printed circuit boards that reduce signal degradation and improve signal integrity at high frequencies. In particular, there is a need for improved via structures for use in multi-layer printed circuit boards.